<!DOCTYPE html>
<title>Test exponentialRampToValueAtTime() with a moderate ratio of change</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script>
'use strict';

promise_test(async function() {
  const bufferSize = 128;
  const sampleRate = 16384;
  // 3 * 2^6, not a power of two, so that there is some rounding error in the
  // exponent
  const rampEndSample = 192;
  // These values are chosen so that there is rounding error in
  // (offset1/offset0)^(1/rampEndSample).
  const offset0 = 4.;
  const offset1 = 7.;
  // 8 units in the last place (ulp) is a generous tolerance if single
  // precision powf() is used.  Math.pow(2, -23) ~ 1 ulp.
  // A simple recurrence relation formulation with only single precision
  // arithmetic applied across the whole rendering quantum would accumulate
  // error up to 50 ulp, losing 5.6 of the 24 bits of precision.
  const relativeTolerance = 8 * Math.pow(2, -23);

  const context = new OfflineAudioContext(1, bufferSize, sampleRate);

  const source = new ConstantSourceNode(context);
  source.start();
  // Explicit event to work around
  // https://bugzilla.mozilla.org/show_bug.cgi?id=1265393
  source.offset.setValueAtTime(offset0, 0.);
  source.offset.exponentialRampToValueAtTime(offset1, rampEndSample/sampleRate);
  source.connect(context.destination);

  const buffer = await context.startRendering();
  assert_equals(buffer.length, bufferSize, "output buffer length");
  const output = buffer.getChannelData(0);
  const ratio = offset1 / offset0;
  for (let i = 0; i < bufferSize; ++i) {
    // Math.pow() uses double precision, while `output` has single precision,
    // but `tolerance` is more than enough to accommodate differences.
    const expected = offset0 * Math.pow(offset1/offset0, i/rampEndSample);
    assert_approx_equals(
      output[i],
      expected,
      relativeTolerance * expected,
      "scheduled value at " + i);
  }
});
</script>
